The present invention relates to heavier than air or lighter than air aircraft where it is desirable for the air vehicle to operate at a higher altitude to stay out of the most effective range of light arms fire and/or to hide behind the natural cloud cover, smoke or atmospheric haze while still being able to get its sensors and targeting systems closer to the ground and beneath the cloud cover, atmospheric haze, fog, smoke, etc. Sensors are also more difficult to make stealthy than other airframe components. This invention also relates to aircraft that want to reduce their signature, draw enemy fire away from the mother aircraft, and/or want to use less expensive non-stealthy sensors without drawing enemy fire to the parent aircraft itself.
The conflict in Kosovo has highlighted a shortfall in the ability to find camouflaged enemy ground forces under cloud cover, haze or smoke. Both manned and unmanned aerial vehicles (UAVs) must drop below the cloud layer to find enemy forces and/or to laser designate them but become vulnerable when they do as illustrated by the loss of a stealth fighter and numerous UAVs.
The closest analogy to the current invention is Northrop""s ROSS (Remotely Operated Sensor System) disclosed in U.S. Pat. No. 5,722,618 dated Mar. 3, 1998. The ROSS system places a sensor stationary near the ground at the end of a long cable below a circling aircraft so as, for example, to get a low enough grazing angle to look into a hangar, under a bridge, etc.
Other somewhat analogous patents are U.S. Pat. Nos. 4,354,419 and 3,362,289.
Until this invention, cloud cover, atmospheric haze, smoke and other phenomena, which obscured visibility, were the most severe naturally occurring limitations to aerial reconnaissance. With this invention these phenomena are turned into an advantage for aerial reconnaissance.
The present invention provides improvements in the survivability of aircraft equipped with sensors/targeting equipment by operating the aircraft in a manner to keep it hidden behind cloud cover or other atmospheric phenomenon that block most sensors while placing the aircraft""s sensors in a pod suspended on a cable below the cloud cover. The sensor pod is much smaller and harder to visually detect than the rest of the airframe and contains only what is necessary to perform its task without a large infrared source like the aircraft""s engine. Even if ground forces are able to detect and shoot at the sensor pod they will be shooting a safe distance aft and below the aircraft and not jeopardizing any flight critical systems. The downing of a stealth fighter in Kosovo has highlighted the fact that even low observable aircraft operating at night are still vulnerable when they drop down below the cloud cover to try to detect targets. Even under circumstances where targets can be detected through the clouds using only a SAR radar for example it is still advantageous to be able to illuminate targets with a laser designator positioned below the cloud layer so laser guided weapons can home in on the target without exposing the aircraft. This laser designator can also be used to illuminate a target to cue other aircraft as to the location of the target which is well known in the art.
Although the current invention can place sensors in a fixed location near the ground and at a low grazing angle relative to an object of interest like the ROSS system the primary purpose of the current invention is to turn cloud cover from a disadvantage for aerial reconnaissance into an advantage by hiding the aircraft behind the clouds and placing the sensors and targeting equipment below the clouds.
The importance of this invention was highlighted during the war in Kosovo with the loss of many UAVs. On one occasion a Predator UAV was shot down and a Hunter UAV was sent over to see what happened to the Predator and it got shot down. Another Hunter was shot down when it was sent over to see what happened to the first two aircraft. Despite the obvious need for a more survivable UAV system no one during or after the Kosovo war thought about using the ROSS system, or unmanned versions of it, to hide the aircraft above or in the clouds and protected from visual and infrared guided weapons while exposing only the sensor pod below the clouds. This was despite the fact that the ROSS system had been flying since at least 1996.
The current invention also differs from ROSS in numerous other ways. The current invention adds a laser designator to the sensor pod to designate targets for laser guided weapons. This laser designator could also be used to cue other aircraft as to the location of the target which is well known in the art. The ROSS system patent proposes every conceivable application for their invention including dropping off humans and taking soil, air or water samples near the target but it never suggests using a laser designator in the pod to designate a target for laser guided bombs or to cue other aircraft. This is probably because they didn""t envision the aircraft above any clouds and unable to designate targets from the aircraft itself and thus putting a laser designator in the pod appeared to add no value. However the experience in Kosovo has caused the Air Force to initiate plans to retrofit laser designators onto all their predator UAVs yet no one during or since Kosovo considered adding a laser designator to the sensor pod of a ROSS system.
Also the ROSS system sensor pod was envisioned as operating near the ground where targets of interest are located and didn""t envision the aircraft operating in or above the clouds. As a result there was no consideration that the cable would be in the clouds and thus would need an anti-ice capability. Also the ROSS system patent also never envisioned sensors and/or methods for making sure the aircraft was hidden and thus protected by the clouds from ground based visual and infrared guided weapons. Also no sensors and/or methods were envisioned for keeping the sensor pod below the clouds and/or not farther below the clouds than necessary to perform their reconnaissance function. Placing the sensor pod farther below the clouds than necessary especially when the aircraft is flying in a straight line to cover more ground significantly increases the cable drag and requires more cable length than necessary. In one embodiment of the current invention cable drag is also reduced by having a power source onboard the sensor pod to eliminate the need to transmit power down the cable and allow a smaller diameter cable.
The ROSS system didn""t address minimizing cable and sensor pod drag since the sensor pod was intended to be used while stationary in the air near the ground observing targets whereas the current invention is intended to be useable by a higher flying aircraft and both while stationary but more often while translating to cover more ground. The ROSS sensor pod was made aerodynamically draggy on purpose to help make the cable more stable during recovery. For the current invention the sensor pod is preferably streamlined to minimize the cable sweep back angle and maximize the vertical separation between the aircraft and the sensor pod in translational flight with a fixed length of cable. The sensor pod also wants to be streamlined because draggy shapes, such as spheres, towed through the air tend to be unstable and jump around resulting in a poor sensor platform. The current invention also preferably uses tail fins on the sensor pod to stabilize it using the airstream and a gimbaled sensor system so that the operator can point the sensors in the desired direction relative to the pod.
The ROSS patent, U.S. Pat. No. 5,722,618, disclosed a circling flight path for the host aircraft to keep the sensor pod stationary. The current invention discloses a zig-zag flight path to be used when a larger vertical separation is desired with a limited length of cable but it is desired to keep translating horizontally at a significant speed without significant vertical oscillations of the pod.
The current invention unlike the ROSS system is also envisioned to achieve some of the advantages of a towed decoy system by reeling the cable out the right distance to draw radar guided weapons away from the aircraft and toward the sensor pod.
Various preferred embodiments of my invention are disclosed herein. Some of them locate laser designators closer and in clearer view of targets than the parent aircraft. Some reduce the signature of the parent aircraft by remotely locating the sensors and/or targeting equipment. Some allow less expensive, less stealthy sensors/targeting equipment without drawing enemy fire to the parent vehicle. Some use the aircraft""s sensors/targeting equipment as a decoy for the parent vehicle. Some provide a streamlined sensor pod with a roll-theta or azimuth-elevation gimbaling system for the sensors. Some minimize the drag and length of the tow cable required in order to place sensors in view of ground targets yet hide the aircraft behind cloud cover.
In accordance with some of the preferred methods of the present invention, a zig-zag flying pattern for the parent aircraft is provided so as to reduce cable drag, and achieve greater vertical separation between the parent aircraft and the sensor pod without excessive vertical oscillations of the sensor pod. In some of the methods, the aircraft is operated to best hide behind or in clouds and a way is provided to minimize the vertical separation between the aircraft and pod and still get the full protection desired.
Other aspects of the invention will best be understood in light of the following descriptions of the best modes for carrying out the invention.